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Title: Optical and electronic properties of PbS colloidal nanocrystals
Author: Elfurawi, Umaima
ISNI:       0000 0004 2726 7354
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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This thesis describes the optical and electrical properties of colloidal PbS nanocrystals synthesized in aqueous solution and comprising different capping ligands and/or matrices. Post-synthesis thermal annealing of thiol-capped PbS colloidal quantum dots (QDs) is discussed and shown to provide a novel means of tailoring the morphological and electronic properties of the QDs. Two different regimes are reported: at low annealing temperatures (< 80oC), the annealing provides a simple strategy for controlling and narrowing the QD size distribution and photoluminescence emission. At higher annealing temperatures, the displacement of the thiol-ligands promotes the fusion of nearby quantum dots thus leading to interconnected nanocrystals. A study of the circularly polarized magneto- photoluminescence of colloidal PbS nanocrystals under the influence of a magnetic field up to 30T is presented. A semiclassical model for the population of polarized excitons is used to account for the measured magnetic field and temperature dependence of the degree of circular polarization of the QD photoluminescence. The g-factor, gX, of the exciton and its dependence on the QD size is reported for the first time. The value of gX increases from 0.1 to 0.3 at low temperature with decreasing the nanocrystal diameter from 9 to 4 nm. The transport properties of a PbS QDs thin film deposited between two electrodes are investigated. This study reveals a non-linear dependence of the current on the applied bias. At low temperature (T<100 K), the conduction is limited by the charging energy (~20 meV) of the quantum dot. The fabrication of a solid-state device based on porous TiO2 impregnated with PbS QDs is discussed. The photovoltaic response of the device in the visible and near infrared wavelength range is obtained by exploiting the Schottky junction that forms at the interface between the PbS/TiO2 film and a metallic contact.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics